It’s my understanding that Li-ion batteries (which a newer tablet likely has) don’t suffer from any type of memory like the older Ni-Cads did. That is, they don’t need to be discharged to near zero, then charged up to 100%.
Having said that, if you’re going to keep it plugged in nearly all the time, it’s not really going to be a concern. My laptop gets unplugged a small handful of times in the rare circumstances that I need to use it in another room (read a recipe, plug it directing into the router etc). Given that, I really don’t care if the battery only lasts 1 or 2 hours instead of 5 or 6.
Something makes me think that the life of a Li-Ion battery is cycle dependet. That is they get X amount of discharges and recharges before the quality drops off. However, those are full cycles., so if it drops to 95% and you charge it back up, that’s only 5% of a cycle. But I could be wrong about that part.
Having said that, even if the battery life totally falls apart, it’ll still work (or should still work) if it’s plugged in. Furthermore, by the time you have battery issues, regardless of how long it takes you’ll probably be in the market for a new one anyway. And, if not, uBreakiFix can likely replace the battery for you (assuming it’s not user serviceable) and you’ll be able to get another few years out of it.